Single and multiple blood bags are commercially available for collecting blood and storing it, or, in the case of multiple bags, for processing the blood under sterile conditions to obtain various blood components that may be desired, for example, packed red cells, plasma, platelets, and cryoprecipitate.
The currently-available blood bags are made of a polyvinyl chloride formulation which includes, as a plasticizer, di-2-ethylhexylphthalate. Such a plasticizer is absolutely necessary for polyvinyl chloride formulations, since polyvinyl chloride itself is not a suitable, flexible plastic material for use in containers. Such blood bags have served extremely well in the storage and processing of blood and blood components, exhibiting a high survival rate with low plasma hemoglobin content after, for example, 21 days of storage at about 4.degree. C.
However, such plasticized blood bags have been found to yield a detectable amount of the ester type plasticizer into the plasma of the blood as it is stored in the bag for a period of days. Typically, blood is stored up to 21 days, but in some special circumstances the storage time of viable blood cells has been extended up to 35 days at conventional storage temperatures. On a typical storage of 21 days, whole blood in a plasticized blood bag may pick up approximately 50 to 80 parts per million of di-2-ethylhexylphthalate per ml., using the commercially available blood bags mentioned above.
While no significant undesirable effects of the di-2-ethylhexylphthalate have been discovered, many physicians and others feel that it would be naturally desirable to keep the concentration of the ester plasticizer which leaches into the blood on storage to a minimum.
Other, chlorine-free plastic formulations have been tested as candidate blood bag materials as well, including flexible polyesters, polyolefins, and the like. As described in Geissler et al U.S. Pat. No. 4,451,259, issued May 29, 1984, filed Dec. 19, 1979 and entitled "Blood Compatible Materials and Medical Devices Made Therefrom", many plastic materials tested without containing ester-type plasticizers have caused blood stored in containers made of such materials under the usual blood storage conditions to exhibit an undesirably high plasma hemoglobin content, indicating that the lysis rate of the red blood cells is high.
It has been determined that the presence of an ester-type plasticizer such as di-2-ethylhexylphthalate in a certain low concentration is effective to suppress the lysis of red blood cells during the long-term storage of blood. Hence, the presence of an ester-type plasticizer, which is an ingredient thought by many to be undesirable because of its leaching characteristics into the blood, turns out to be a valuable component for blood storage to suppress red cell hemolysis.
In accordance with this invention, a method of storing a quantity of red blood cells is provided, in which the desirable effects of the blood extractable ester plasticizer in suppressing hemolysis on storage may be exploited, while at the same time a minimum desired concentration of the extractable ester-type plasticizer necessary to accomplish this end is provided. The method uses a polyvinyl chloride blood bag having the desired properties of softness, strength and collapsibility, using only the minimal concentration of extractable plasticizer necessary to achieve the desired antihemolytic effect.
By this invention, for the first time polyvinyl chloride blood bags may be used to minimize both hemolysis and exposure to blood extractable plasticizers, having been formulated to their optimum physical characteristics using a sufficient concentration of two plasticizers for that purpose, the concentration of a plasma-extractable, hemolysis-suppressing plasticizer being present at a lesser, optimum concentration to provide the desired amount of red cell hemolysis suppression, so that overall exposure to the plasticizer materials by a patient may be minimized.